Respuesta :
204 amu is the relative atomic mass of thallium
Isotopes of Thallium and % abundances
Tl-203 : 29.5%
Tl-205: 70.5%
Formula:
Relative atomic mass = Σ(Isotope-mass x abundance)/100
It is given by the summation of the product of all the isotope masses and their % abundances
For Thallium:
Relative atomic mass = (203 x 29.5 +205 x 70.5)/100 = 204
Since the number of significant digits is 3, the relative atomic mass = 204 amu
What is relative atomic mass ?
A dimensionless physical quantity known as relative atomic mass (symbol: Ar) or atomic weight is defined as the ratio of the average mass of atoms of a chemical element in a particular sample to the atomic mass constant. The mass of an atom of carbon-12 is one-twelfth of the atomic mass constant, or mu (symbol).
Since the ratio's two components are masses, the final number has no dimensions, which is why it is referred to as relative.
The weighted arithmetic mean of the masses of the individual atoms (including their isotopes) that are present in the sample is the relative atomic mass of a certain element for a specific sample. This amount can vary greatly between samples since the origin of the sample (and therefore its radioactive or diffusion history) may have caused different isotopic abundance combinations.
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